Think you know the story of Zola Budd? Even if you remember how the barefoot prodigy broke world records, became a symbol of South Africa's oppression, and was blamed for Mary Decker's Olympic nightmare, there's more to her story than the legend.

What really improves performance? Intense training sessions—as long as you do them right. So we asked elites who run hard several times a week to explain how you can get the most out of your quality workouts.